These Altmount Kits by Balmar offer the opportunity to install a larger alternator than would otherwise be possible. This kit is for the Westerbeke 18, 21A, 27A, 35B, 38B, 42B See the "Additional Information" tab for details and photos of an actual installation. Alternator upgrades using a single drive belt are limited by the amount of power that can be transferred by the belt but using a multi grooved belt considerably increases the possibilities. The kits include a set of serpentine pulleys for the crankshaft, water pump pulley and alternator. This pulley kit comes with two belts so you have a spare, the alternators need to be purchased separately. If you order an alternator at the same time as the kit it will come with the appropriate pulley pre-installed.